Filter to trigger landscape-format pages in PDF

[ryangyoung]

As a tech writer, I want to print pages that have large tables or other very wide content as landscape pages in the PDF output so that the content is easier to read.

It looks like Prince has this ability: https://www.princexml.com/doc/paged/#idp47329831479296

But to be really usable, it would need to be a flag or something similar in Dactyl.

Acceptance Criteria

• Dactyl can output PDF with selected pages as landscape
• Writer can mark section that should be printed as landscape through a build argument or config flag

link to original jira ticket: https://ripplelabs.atlassian.net/browse/DOC-660

[ryangyoung]

The way this currently works is that we add the following in the .md file:

<div class="landscape-content">
<b>Request</b>
<div class="split-code-left">
<p><b>v2.6.3</b></p>
<pre><code>
content
</code></pre>
</div>
<div  class="split-code-right">
<p><b>v3.0.0</b></p>
<pre><code>
content
</code></pre>
</div>
</div>

This commit shows what was added to pdf.css: https://github.com/ripple/docs-private/commit/edd632c3cbadca20c90e1cbb179b42af75c661d1#diff-da89956dc4e154ac0e2ef24058dac63fR46

For a full example, see: https://github.com/ripple/docs-private/tree/master/documents/ripple-solution/delta